Submitted to: Applied and Environmental Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/9/2008
Publication Date: 11/1/2008
Citation: Liu, Y., Ream, A.R. 2008. Gene Expression Profiling of Listeria Monocytogenes Strain F365 during Growth in Ultrahigh-Temperature-Processed Skim Milk. Applied and Environmental Microbiology. 74(22):6859-6866. Interpretive Summary: The bacterium Listeria monocytogenes is an important food-borne pathogen that causes disease in humans and animals. This bacterium was able to grow and survive at food storage conditions such as refrigeration temperatures, low pH and high salt. However, the factors contributing to the survival and growth of this bacterium in food remain unclear. Microarray technology, a new technology that can be used to study the bacterium at the genome level, was used to study the behavior of L. monocytogenes in skim milk and a synthetic medium. Genes that were identified by the microarray assay were verified by real-time reverse transcriptase- polymerase chain reaction (RT-PCR) assays. Information from this study will help understanding how L. monocytogenes survive in skim milk, eventually aid developing new intervention strategies to control this bacterium in food.
Technical Abstract: To study how L. monocytogenes survives and grows in milk, microarray technology was used to monitor the gene expression profiles of L. monocytogenes strain F2365 in UHT pasteurized skim milk. Total RNA was isolated from strain F2365 in UHT pasteurized skim milk after 24 hours at 4 degree C, and labeled with fluorescent dyes and hybridized to commercial oligonucleotide (35-mers) microarray chips containing the whole genome of L. monocytogenes 4b. Compared to L. monocytogenes grown in Brain Heart infusion (BHI) for 24 hours at 4 degree C, 26 genes were up-regulated (> 2-fold) in UHT pasteurized skim milk, while 14 genes were down-regulated (< -2-fold). The up-regulated genes included genes encoding for transport and binding, transcriptional regulator, proteins in amino acid biosynthesis and energy metabolism, protein synthesis, toxin production and resistance, cell division, and hypothetical proteins, whereas the down-regulated genes included genes that encode for transport and binding, protein synthesis, cellular processes, cell envelope, energy metabolism, and a transcriptional regulator and a unknown protein. The gene expression changes determined by microarray assays were confirmed by real-time RT-PCR analyses. Cells of L. monocytogenes in skim milk displayed the same sensitivity to oxidative stress as the cells grown in BHI medium. This study represents the first report on the global transcriptional gene expression profiling of L. monocytogenes in liquid food.